1. Field of the Invention
The present invention relates to an improved data coding method of an optical disk for realizing a high data transfer rate and a high density by simultaneously reproducing dual spiral tracks with one beam of light.
2. Description of the Related Art
In general, a read only optical disk such as a CD-ROM, a DVD-ROM, etc., has recorded information on a single spiral track 1 on a recording surface thereof, as shown in FIG. 1. The information signals are recorded in binary form depending on whether a pit 3 is formed or not and the length of each one of the pits 3 formed in a depressed form to have a predetermined depth.
In other words, '0' and '1' states are classified by the difference in the intensity of diffracted beams between portions at the ends of each pit 3 and other portions, detected by an optical pickup (not shown), and the information signals are recorded or reproduced by coding or decoding those states.
In the optical disk as described above, since the size of a disk, the distance between neighboring tracks depending on the light spot size focused on the track, the minimum length of the pits, etc., are limited, there is a limit to increasing recording density.
In addition, there is a disadvantage to reading the optical disk in that the read time is long. When a CD-ROM having a storage capacity of 0.65 giga bytes per side is read at a linear speed of 28.8 m/s and a clock frequency of about 100 MHz, it takes more than 3 minutes. When a DVD-ROM having a storage capacity of 4.7 giga bytes per side is read at a linear speed of 6.98 m/s and a clock frequency of about 58.36 MHz, it takes more than 22 minutes.
The inventors have discovered the above-noted problems and have developed solutions to these problems.